doctrine:mapping:convert on entities without primary key

It issn't possible to use some of the Doctrine tools on entities without primary key.
Following error appears:

PHP Fatal error: Call to a member function getColumns() on a non-object in /media/sf_webdev-shared/Symfony/vendor/doctrine/lib/Doctrine/ORM/Mapping/Driver/DatabaseDriver.php on line 133

DatabaseDriver tries to get primary key columns without checking if there is any primary key.